This invention relates generally to a process which is employed in manufacturing semiconductor chips. More particularly, the invention relates to a process for improving the structural properties of certain porous materials that are utilized as integrated circuit (IC) dielectrics.
New materials with low dielectric constants (known in the art as “low-k dielectrics”) are being investigated for their potential use as insulators in semiconductor chip designs. A low dielectric constant material aids in enabling further reductions in integrated circuit feature dimensions. The substance with the lowest dielectric constant is air (k=1.0). Therefore, porous dielectrics are very promising candidates since they have the potential to provide very low dielectric constants. Unfortunately, however, such porous low-k dielectrics typically have the problem of insufficient mechanical strength.
Thin film dielectric coatings on electric devices are known in the art. For instance, U.S. Pat. Nos. 4,749,631 and 4,756,977, to Haluska et al., disclose silica based coatings produced by applying solutions of silicon alkoxides or hydrogen silsesquioxane, respectively, to substrates and then heating the coated substrates to a temperature between 200 and 1000° C. The dielectric constant of these coatings is often too high for certain electronic devices and circuits.
U.S. Pat. Nos. 4,847,162 and 4,842,888, to Haluska et al., teach the formation of nitrided silica coatings by heating hydrogen silsesquioxane resin and silicate esters, respectively, to a temperature between 200 and 1000° C. in the presence of ammonia.
Glasser et al., Journal of Non-Crystalline Solids, 64 (1984) pp. 209-221, teaches the formation of ceramic coatings by heating tetraethoxysilane in the presence of ammonia. This reference teaches the use of anhydrous ammonia and that the resulting silica coatings are nitrided.
U.S. Pat. No. 4,636,440, to Jada, discloses a method of reducing the drying time for a sol-gel coated substrate comprising exposing the substrate to aqueous quaternary ammonium hydroxide and/or alkanol amine compounds. Jada requires that the coating be dried prior to heating. It is specifically limited to hydrolyzed or partially hydrolyzed silicon alkoxides.
U.S. Pat. No. 5,262,201, to Chandra et al., and U.S. Pat. No. 5,116,637, to Baney et al., teach the use of basic catalysts to lower the temperature necessary for the conversion of various preceramic materials, all involving hydrogen silsesquioxane, to ceramic coatings. These references teach the removal of solvent before the coating is exposed to the basic catalysts.
U.S. Pat. No. 5,547,703, to Camilletti et al., teaches a method for forming low dielectric constant Si—O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin successively under wet ammonia, dry ammonia, and oxygen. The resultant coatings have dielectric constants as low as 2.42 at 1 MHz. This reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,523,163, to Balance et al., teaches a method for forming Si—O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin to convert it to a Si—O containing ceramic coating and then exposing the coating to an annealing atmosphere containing hydrogen gas. The resultant coatings have dielectric constants as low as 2.773. The reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,618,878, to Syktich et al., discloses coating compositions containing hydrogen silsesquioxane resin dissolved in saturated alkyl hydrocarbons useful for forming thick ceramic coatings. The alkyl hydrocarbons disclosed are those up to dodecane. The reference does not teach exposure of the coated substrates to basic catalysts before solvent removal.
U.S. Pat. No. 6,231,989, to Chung et al., entitled “METHOD OF FORMING COATINGS” discloses a method of making porous network coatings with low dielectric constants. The method comprises depositing a coating on a substrate with a solution comprising a resin containing at least 2 Si—H groups and a solvent in a manner in which at least 5 volume % of the solvent remains in the coating after deposition. The coating is then exposed to an environment comprising a basic catalyst and water. Finally, the solvent is evaporated from the coating to form a porous network. If desired, the coating can be cured by heating to form a ceramic. Films made by this process have dielectric constants in the range of 1.5 to 2.4 with an elastic modulus between about 2 and about 3 GPa.
Porous low-k dielectric materials produced by spin-on and chemical vapor deposition processes typically require a curing process subsequent to the deposition. Typical process conditions for curing these low-k films include nitrogen purged furnace anneals at temperatures between about 350 and about 450° C. for 30 to 180 minutes. As was described in U.S. patent application Ser. Nos. 09/681,332, 09/952,649, 09/906,276 and 09/952,398, the disclosures of which are incorporated herein by reference, instead of thermally curing and plasma treating, porous network coatings can be plasma or UV cured, eliminating the need for prior furnace curing.
However, there remains a need for a process for making a porous low-k material with improved structural properties, such as an improved elastic modulus and material hardness, without compromising or deteriorating its electrical properties.